Tonight, a new and revealing clue more than three years after that devastating air france crash into the atlantic. We learned more this evening about the captain from the black box recorder. And he talks about his lack of sleep, flying the jumbo jet on just one hour of sleep. Abc's reena ninan tonight. Reporter: The plane was designed to be incapable of stalling, basically pilot-proof. But air france flight 447 traveling from rio de janiero to paris, ended in the atlantic ocean in 2009, killing all 288 on board. Only two years later would the flight recorder be found, showing the plane crashed from equipment problems that disengaged the autopilot in a storm. Leaving a young, insufficiently trained crew unable to manually fly the plane. And this weekend, a new french news magazine reporting shortly after take off, the pilot said in the cockpit. I didn't sleep enough last night. One hour. It's not enough. In fact, the pilot was on a rest break when the trouble started. He returned to find chaos in the cockpit. French authorities have refused to release the entire black box transcript. Abc's elizabeth vargas questioned the decision. Why did you leave parts out? Well, you know, you have some personal conversations that is not useful to understand the accident.

This transcript has been automatically generated and may not be 100% accurate.

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